Python in a Nutshell, 2nd Edition

DBM Modules

A DBM-like file is a file that contains pairs of strings (key,data), with support for fetching or storing the data given a key, known as keyed access. DBM-like files were developed on early Unix systems, with functionality roughly equivalent to that of access methods popular on mainframe and minicomputers of the time, such as ISAM, the Indexed-Sequential Access Method. Today, many libraries, available for many platforms, let programs written in many different languages create, update, and read DBM-like files.

Keyed access, while not as powerful as the data access functionality of relational databases, may often suffice for a program’s needs. If DBM-like files are sufficient, you may end up with a program that is smaller and faster than one using an RDBMS.

The classic dbm library, whose first version introduced DBM-like files many years ago, has limited functionality but tends to be available on many Unix platforms. The GNU version, gdbm, is richer and very widespread. The BSD version, dbhash, offers superior functionality. Python supplies modules that interface with each of these libraries if the relevant underlying library is installed on your system. Python also offers a minimal DBM module, dumbdbm (usable anywhere, as it does not rely on other installed libraries), and generic DBM modules, which are able to automatically identify, select, and wrap the appropriate DBM library to deal with an existing or new DBM file. Depending on your platform, your Python distribution, ...